There have already been known a number of methods and apparatuses for producing a resin-impregnated structure reinforced with continuous fibers by contacting, in a zigzag pattern, a continuous fiber bundle serving as a reinforcing material with the surfaces of a plurality of opening means arranged in series within an apparatus for opening and resin-impregnation (or by making them run around the means) and simultaneously impregnating the opened (or loosed) continuous fibers with a molten resin. For instance, a variety of techniques are disclosed in the patent publication listed below.
It can be understood from the disclosures thereof that continuous fiber bundles are brought into contact with (opening) pins or (opening) rolls for opening and resin-impregnation of the continuous fiber bundle, in either of these techniques. It has been proven that, as a result, the continuous fibers are damaged to a substantial extent, that this in turn leads to the formation of fluff and that it is thus difficult to stably produce resin-impregnated structures reinforced with continuous fibers. Each publication will hereinafter be described in more detail.
(R1) Japanese Patent Publication No. 63 (1988)-37694 (gazetted specification) and the Related Written Decision (Trial Case No. 2 (1990)-17153).
The gazetted specification and the written decision disclose or propose a method which comprises passing, under tension, reinforcing fiber bundles arranged in a band-like pattern through a spreader while bringing the bundles into contact with the surface of the spreader, and while supplying a thermoplastic polymer having a melt viscosity of less than 100 Ns/m.sup.2 to a nip formed between the reinforcing fiber bundles and the spreader, to thus impregnate the fiber bundles with the polymer.
(R2) Japanese Patent Laid-Open Publication No. 63 (1988)-264326 (gazetted Specification)
In this gazetted specification, there is proposed a method for impregnation, which comprises arranging or spreading fiber bundles in a web-like (this term is identical to "band-like") pattern, then coating the bundles with a molten resin and thereafter passing the coated fiber bundles through a specific zigzag barrier region within an apparatus for opening and resin-impregnation.
(R3) Japanese Examined Patent Publication No. 5 (1993)-68327 (gazetted specification)
This gazetted specification proposes a method for impregnation, which comprises extruding a molten resin through the tip of a bow head of an extruder and simultaneously passing a series of fibers, under tension, through the bow head while bringing the fibers into contact with the bow head.
(R4) Japanese Patent Laid-Open Publication No.4 (1992)-278311 (gazetted specification)
This gazetted specification proposes an impregnation method in which a choking structure is provided in the course of a flow path for fibers in an apparatus for opening and resin-impregnation and the fibers are brought into contact with the choking structure to thus subject the fibers to opening and to simultaneously impregnate them with a resin.
&lt;Inventors' View on (R1) to (R4)&gt;
These methods can certainly provide resin-impregnated structures uni-directionally reinforced, which are excellent in resin-impregnation ability. In all of these methods, however, the fibers would severely be damaged since the reinforcing fiber bundles pass through (around) pins or projected portions while bringing the bundles into contact with the pins or projections. It has been found that, as a result, the methods have a problem that fluffs are easily formed due to breakage of fibers. The formation of fluffs would impair any stable productivity of the intended resin-impregnated structure and ultimately leads to the interruption of the apparatus for opening and resin-impregnation.
(R5) Japanese Patent Laid-Open Publication No. 6 (1994)-254857 (gazetted specification)
This gazetted specification proposes an impregnation method which comprises pressing fiber bundle through a die box while pressing it against rotatable rolls positioned within the die box in a zigzag pattern to thus induce opening of the fiber bundle and then supplying a resin to opened the fibers, to thereby impregnating it with the resin.
This method is designed so as to reduce the damage to the fibers by rotating the rolls, and permits an increase in the take-off speed to a certain extent (20 m/min). As a result of investigations, however, the fiber bundles are likewise brought into contact with the rolls (or pressed against the rolls), while applying a tension thereto in this method as well. Accordingly, it has been found that this method is accompanied by the easy formation of fluffs and that it is still difficult to ensure stable productivity.
(R6) Japanese Patent Laid-Open Publication No. 6 (1994)-91645 (gazetted specification)
This gazetted specification proposes an impregnation method which comprises supplying fiber bundles to an S-shaped die so that the fiber bundles pass through (around) the projected portions in the S-shaped region under the action of a tension while bringing the bundles into contact therewith and simultaneously discharging a molten resin through discharge openings formed on the tips of the projected portions to thus stepwise impregnate the bundles at three positions.
(R7) Japanese Patent Laid-Open Publication No. 6 (1994)-143440 (gazetted specification)
This gazetted specification proposes an impregnation method which comprises heating the reinforcing fibers in advance, then coating them with a molten resin and passing the fibers through (around) at least 8 projected portions which are arranged alternately while bringing the fibers into contact therewith.
It has been said that these methods described in references (R6) and (R7) permit the achievement of a take-off speed of not less than 20 m/min because of the improved means such as the means for stepwise impregnation of the reinforcing fibers and for heating the fibers in advance.
However, it has been found that these methods are often accompanied by the formation of fluffs. Therefore, it is difficult to ensure stable productivity. This would be because the fiber bundles are passed through (around) the projected portions under tension thereto while bringing the bundles into contact therewith.
(R8) Japanese Patent Laid-Open Publication No. 63 (1989)-132036 (gazetted specification)
This gazetted specification proposes an impregnation method which comprises mechanically impregnating reinforcing fiber bundles with a resin by supplying the fiber bundles provided with the resin to the space formed between upper and lower rolls within an apparatus for opening and resin-impregnation to thus press the bundles.
(R9) Japanese Patent Laid-Open Publication No. 1 (1989)-208118 (gazetted specification)
This gazetted specification proposes an impregnation method which comprises mechanically impregnating reinforcing fiber bundles with a resin by pressing the fiber bundles provided with the resin using upper and lower rolls, i.e., a combination of a convex roll and a concave roll, within an apparatus for opening and resin-impregnation.
With respect to (R8) and (R9) in each of the foregoing techniques, both of the opening of continuous fiber bundles and the impregnation of the resulting opened fiber bundles with a resin are performed by the compressive force acting on the bundles only at the contact point between the upper and lower rolls and accordingly, the contact time between the fibers and the rolls is quite short even if using at least two pairs of rolls. As a result, it has been found that there still remains room for improvement in the impregnating ability. In addition, the fiber bundles are directly pressed by upper and lower rolls, the bundles are thus severely damaged during the opening thereof. As a result, it has been found that the fibers undergoes form fluffs and productivity is lowered.